Add InterpreterPattern.

chrish · chrish · commit ac1fd7b18f0b · 2017-10-24T16:17:17.000+08:00
diff --git a/Behavioral/InterpreterPattern/src/io/csie/chris/Evaluator.java b/Behavioral/InterpreterPattern/src/io/csie/chris/Evaluator.java
@@ -0,0 +1,39 @@
+package io.csie.chris;
+
+import io.csie.chris.expression.Expression;
+import io.csie.chris.expression.Minus;
+import io.csie.chris.expression.Plus;
+import io.csie.chris.expression.Variable;
+
+import java.util.Map;
+import java.util.Stack;
+
+public class Evaluator implements Expression {
+
+    private Expression syntaxTree;
+
+    public Evaluator(final String expression) {
+
+        final Stack<Expression> expressionStack = new Stack<Expression>();
+
+        for (final String token : expression.split(" ")) {
+            if (token.equals("+")) {
+                final Expression subExpression = new Plus(expressionStack.pop(), expressionStack.pop());
+                expressionStack.push(subExpression);
+            } else if (token.equals("-")) {
+                // it's necessary remove first the right operand from the stack
+                final Expression right = expressionStack.pop();
+                // ..and after the left one
+                final Expression left = expressionStack.pop();
+                final Expression subExpression = new Minus(left, right);
+                expressionStack.push(subExpression);
+            } else
+                expressionStack.push(new Variable(token));
+        }
+        syntaxTree = expressionStack.pop();
+    }
+
+    public int interpret(final Map<String, Expression> context) {
+        return syntaxTree.interpret(context);
+    }
+}
diff --git a/Behavioral/InterpreterPattern/src/io/csie/chris/Main.java b/Behavioral/InterpreterPattern/src/io/csie/chris/Main.java
@@ -0,0 +1,27 @@
+package io.csie.chris;
+
+import io.csie.chris.expression.Expression;
+import io.csie.chris.expression.Number;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class Main {
+
+    public static void main(final String[] args) {
+
+        final String expression = "w x z - +";
+
+        final Evaluator sentence = new Evaluator(expression);
+
+        final Map<String, Expression> variables = new HashMap<>();
+
+        variables.put("w", new Number(5));
+        variables.put("x", new Number(10));
+        variables.put("z", new Number(42));
+
+        final int result = sentence.interpret(variables);
+
+        System.out.println(result);
+    }
+}
diff --git a/Behavioral/InterpreterPattern/src/io/csie/chris/expression/Expression.java b/Behavioral/InterpreterPattern/src/io/csie/chris/expression/Expression.java
@@ -0,0 +1,8 @@
+package io.csie.chris.expression;
+
+import java.util.Map;
+
+public interface Expression {
+
+    int interpret(final Map<String, Expression> variables);
+}
diff --git a/Behavioral/InterpreterPattern/src/io/csie/chris/expression/Minus.java b/Behavioral/InterpreterPattern/src/io/csie/chris/expression/Minus.java
@@ -0,0 +1,19 @@
+package io.csie.chris.expression;
+
+import java.util.Map;
+
+public class Minus implements Expression {
+
+    private Expression leftOperand;
+
+    private Expression rightOperand;
+
+    public Minus(final Expression left, final Expression right) {
+        leftOperand = left;
+        rightOperand = right;
+    }
+
+    public int interpret(final Map<String, Expression> variables) {
+        return leftOperand.interpret(variables) - rightOperand.interpret(variables);
+    }
+}
diff --git a/Behavioral/InterpreterPattern/src/io/csie/chris/expression/Number.java b/Behavioral/InterpreterPattern/src/io/csie/chris/expression/Number.java
@@ -0,0 +1,16 @@
+package io.csie.chris.expression;
+
+import java.util.Map;
+
+public class Number implements Expression {
+
+    private int number;
+
+    public Number(final int number) {
+        this.number = number;
+    }
+
+    public int interpret(final Map<String, Expression> variables) {
+        return number;
+    }
+}
diff --git a/Behavioral/InterpreterPattern/src/io/csie/chris/expression/Plus.java b/Behavioral/InterpreterPattern/src/io/csie/chris/expression/Plus.java
@@ -0,0 +1,19 @@
+package io.csie.chris.expression;
+
+import java.util.Map;
+
+public class Plus implements Expression {
+
+    private Expression leftOperand;
+
+    private Expression rightOperand;
+
+    public Plus(final Expression left, final Expression right) {
+        leftOperand = left;
+        rightOperand = right;
+    }
+
+    public int interpret(final Map<String, Expression> variables) {
+        return leftOperand.interpret(variables) + rightOperand.interpret(variables);
+    }
+}
diff --git a/Behavioral/InterpreterPattern/src/io/csie/chris/expression/Variable.java b/Behavioral/InterpreterPattern/src/io/csie/chris/expression/Variable.java
@@ -0,0 +1,19 @@
+package io.csie.chris.expression;
+
+import java.util.Map;
+
+public class Variable implements Expression {
+
+    private String name;
+
+    public Variable(final String name) {
+        this.name = name;
+    }
+
+    public int interpret(final Map<String, Expression> variables) {
+        if (null == variables.get(name))
+            return 0; // Either return new Number(0).
+
+        return variables.get(name).interpret(variables);
+    }
+}
